Methods for purifying and recycling lead from spent lead-acid batteries

ABSTRACT

The present disclosure relates to methods by which lead from spent lead-acid batteries may be extracted, purified, and used in the construction of new lead-acid batteries. A method includes: (A) forming a mixture including a carboxylate source and a lead-bearing material; (B) generating a first lead salt precipitate in the mixture as the carboxylate source reacts with the lead-bearing material; (C) increasing the pH of the mixture to dissolve the first lead salt precipitate; (D) isolating a liquid component of the mixture from one or more insoluble components of the mixture; (E) decreasing the pH of the liquid component of the mixture to generate a second lead salt precipitate; and (F) isolating the second lead salt precipitate from the liquid component of the mixture. Thereafter, the isolated lead salt precipitate may be converted to leady oxide for use in the manufacture of new lead-acid batteries.

CROSS-REFERENCE

This application claims is a divisional of U.S. patent application Ser.No. 14/498,748, entitled, “METHODS FOR PURIFYING AND RECYCLING LEAD FROMSPENT LEAD-ACID BATTERIES,” filed Sep. 26, 2014, which claims priorityfrom and the benefit of U.S. Provisional Application Ser. No.62/015,045, entitled “METHODS FOR PURIFYING AND RECYCLING LEAD FROMSPENT LEAD-ACID BATTERIES”, filed Jun. 20, 2014, U.S. ProvisionalApplication Ser. No. 62/015,042, entitled “SYSTEMS AND METHODS FORPURIFYING AND RECYCLING LEAD FROM SPENT LEAD-ACID BATTERIES”, filed Jun.20, 2014, U.S. Provisional Application Ser. No. 62/015,058, entitled“SYSTEMS AND METHODS FOR CLOSED-LOOP RECYCLING OF A LIQUID COMPONENT OFA LEACHING MIXTURE WHEN RECYCLING LEAD FROM SPENT LEAD-ACID BATTERIES”,filed Jun. 20, 2014, U.S. Provisional Application Ser. No. 62/015,070,entitled “SYSTEMS AND METHODS FOR SEPARATING A PARTICULATE PRODUCT FROMPARTICULATE WASTE WHEN RECYCLING LEAD FROM SPENT LEAD-ACID BATTERIES”,filed Jun. 20, 2014, which are hereby incorporated by reference for allpurposes.

BACKGROUND

The present disclosure relates generally to systems and methods forrecycling spent lead-acid batteries, and more specifically, relates topurifying and recycling the lead content of lead-acid batteries.

The lead used in the manufacture of the active material of new lead-acidbatteries is typically in the form of lead oxide (PbO) that is typicallyproduced by oxidizing a lead source having a high purity (e.g., 99.95%Pb). Lead oxide of high-purity is generally desirable when manufacturinglead-acid batteries since certain impurities (e.g., antimony, bariumsulfate, tin) may enable side-reactions that can significantly affectbattery cell performance. While it may be desirable to attempt torecover lead from the waste of spent or retired lead-acid batteries,this material may include a variety of lead compounds (lead alloys,oxides, sulfates and carbonates) and an array of physical and/orchemical impurities. Existing methods for purifying lead typically relyalmost entirely on multi-stage pyrometallurgical smelting in which someof these compounds are combusted to produce volatile gases, some ofwhich must be scrubbed (e.g., captured and removed from the exhauststream) to prevent release, in accordance with environmentalregulations, and subsequently the remaining impurities are removed fromthe metallic lead in various refining operations. Since these operationsoften require specialized equipment and certain consumables (e.g.,solutions or other refining agents), this refinement process generallyadds cost and complexity to the lead recovery process.

SUMMARY

The present disclosure relates to methods by which lead from spentlead-acid batteries may be extracted, purified, and used in theconstruction of new lead-acid batteries. In an embodiment, a methodincludes: (A) forming a mixture including a carboxylate source and alead-bearing material; (B) generating a first lead salt precipitate inthe mixture as the carboxylate source reacts with the lead-bearingmaterial; (C) increasing the pH of the mixture to dissolve the firstlead salt precipitate; (D) isolating a liquid component of the mixturefrom one or more insoluble components of the mixture; (E) decreasing thepH of the liquid component of the mixture to generate a second lead saltprecipitate; and (F) isolating the second lead salt precipitate from theliquid component of the mixture.

In another embodiment, a method includes, (A) forming a mixtureincluding a hydroxide and a lead-bearing material, wherein the pH of themixture is greater than 7 and a temperature of the mixture is between30° C. and 100° C.; (B) isolating a liquid component of the mixture fromone or more insoluble components of the mixture; (C) adding acarboxylate source to the liquid component to decrease the pH of theliquid component and generate a lead salt precipitate; and (D) isolatingthe lead salt precipitate from the liquid component.

In another embodiment, a method includes reacting one or more impuritiesof a lead salt solution with at least one compound to evolve one or moreimpurity gases that are released from the lead salt solution. Further,the one or more impurities comprise an element or compound of Group 14,an element or compound of Group 15, an element or compound of Group 16,an element or compound of Group 17, or a combination thereof.

In another embodiment, a method includes, (A) forming a mixtureincluding a carboxylate source and a lead-bearing material; (B)generating a first lead salt precipitate in the mixture as thecarboxylate source reacts with the lead-bearing material; (C) increasingthe pH of the mixture to dissolve the first lead salt precipitate; (D)isolating a liquid component of the mixture from one or more insolublecomponents of the mixture; (E) adding an antisolvent to the liquidcomponent to generate a second lead salt precipitate; and (F) isolatingthe second lead salt precipitate from the liquid component of themixture.

DRAWINGS

FIG. 1 is a flow diagram illustrating an embodiment of a process bywhich lead from spent lead-acid batteries may be extracted, purified,and used in the construction of new lead-acid batteries;

FIG. 2 is an X-ray diffraction (XRD) pattern of a lead citrateprecipitate for an embodiment of the present approach;

FIG. 3 is a flow diagram illustrating an embodiment of an alternativeprocess by which lead from spent lead-acid batteries may be extracted,purified, and used in the construction of new lead-acid batteries;

FIG. 4 is a flow diagram illustrating an embodiment of an alternativeprocess by which lead from spent lead-acid batteries may be extracted,purified, and used in the construction of new lead-acid batteries;

FIG. 5 is an X-ray diffraction (XRD) pattern of an embodiment of theleady oxide product formed via calcination of the recovered lead salt;and

FIG. 6 is an X-ray diffraction (XRD) pattern of another embodiment ofthe lead oxide product formed via base treatment of the recovered leadsalt.

DETAILED DESCRIPTION

One or more specific embodiments will be described below. In an effortto provide a concise description of these embodiments, not all featuresof an actual implementation are described in the specification. Itshould be appreciated that in the development of any such actualimplementation, as in any engineering or design project, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which may vary from one implementation toanother. Moreover, it should be appreciated that such a developmenteffort might be complex and time consuming, but would nevertheless be aroutine undertaking of design, fabrication, and manufacture for those ofordinary skill having the benefit of this disclosure.

When introducing elements of various embodiments of the presentdisclosure, the articles “a,” “an,” and “the” are intended to mean thatthere are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.Additionally, it should be understood that references to “oneembodiment” or “an embodiment” of the present disclosure are notintended to be interpreted as excluding the existence of additionalembodiments that also incorporate the recited features.

As used herein, the disclosure of a particular component being made ofor including a particular element called out by name (e.g., lead),should be interpreted to encompass all forms of lead (e.g., metalliclead, lead compounds, or mixtures thereof). For distinction, as usedherein, the disclosure of a metallic form of an element may be indicatedby the chemical formula (e.g., Pb(0)) or using the terms elemental,metallic, or free (e.g., elemental lead, metallic lead, or free lead).As used herein, “leady oxide” may be used to indicate a mixture ofmetallic lead (e.g., Pb(0)) and lead oxide (e.g., PbO) in various ratiosas described. As used herein, the term “substantially free” may be usedto indicate that the identified component is not present at all, or isonly present in a trace amount (e.g., less than 0.1%, less than 0.01%,or less than 0.001%). As used herein, “an element or compound of GroupX” may refer to any chemical substance (e.g., element or compound) thatincludes an element from the identified column of the periodic table.For example, “an element or compound of Group 14” may include any of theelements from Group 14 (e.g., carbon, silicon, tin, etc.) as well as anycompounds that include Group 14 elements (e.g., carbonates, silicates,stannates, etc.). As used herein, a “carboxylate source” is any moleculeor polymer that includes at least one carboxylate or carboxylic acidmoiety or functionality. Accordingly, a non-limited list of examplecarboxylate sources include: citric acid, acetic acid, formic acid,citrate, acetate, formate, dilactate, oxalate, tartarate, or anycombination thereof. The term “citrate” herein refers to citric acid, ora citrate salt of a Group 1 or Group 2 metal, or ammonium citrate. Theterm “acetate” herein refers to acetic acid, or acetate salts of a Group1 or Group 2 metal, or ammonium acetate. “New lead-acid battery” hereinrefers to a newly produced lead acid battery, while the term “spentlead-acid battery,” also referred to as a battery core, indicates abattery at the end of its useable service life. As used herein, an“antisolvent” is a solvent that may be added to a solution to facilitatethe precipitation of a dissolved component (e.g., a lead salt). As usedherein “peroxide” refers to hydrogen peroxide and/or any organicperoxide (e.g. peracetic acid). The term “hydroxide” herein indicates aGroup 1 or Group 2 metal hydroxide, ammonium hydroxide, or ammonia gasintroduced into the reaction mixture to form ammonium hydroxide in-situ,or combinations thereof.

As mentioned above, existing methods typically rely heavily onpyrometallurgical smelting or combustion to recover and purify lead fromspent lead-acid batteries. For such methods, the lead-bearing materialfrom spent lead-acid batteries, which may include a number of leadcompounds and a number of impurities, may be heated such that at least aportion of the impurities may combust or volatilize and be released asbyproducts. Additionally, after pyrometallurgical smelting or combustionof the lead-bearing material, such methods may involve subsequentrefinement steps to remove byproducts or other impurities to yieldpurified lead. Since the atmospheric release of some of these combustionbyproducts (e.g., SO₂, soot) may be restricted by local environmentalregulations, present embodiments are directed toward enabling asolution-based removal of several impurities from the recovered lead,thereby avoiding or reducing the formation of such combustion byproductsand/or the cost associated with scrubbing them from the exhaust stream.Additionally, present embodiments address limitations of other wastelead purification techniques, enabling a robust technique for purifyingand recycling of recovered lead on an industrial scale. That is, thepresently disclosed technique is robust such that entire spent lead-acidbatteries may be processed (e.g., broken apart, ground, or milled) andsupplied as input, and, from this assorted mixture, the disclosedprocesses enable the formation of pure leady oxide for use in newlead-acid batteries. Accordingly, present embodiments enable a leadpurification technique that is robust to the presence of a wide varietyof impurities and provides enhanced control over the parameters of thepurification process, while obviating or limiting reliance onconventional smelting and refining steps for purification and limitingthe combustion of impurities.

FIG. 1 is a flow diagram illustrating an embodiment of a process 10 bywhich lead from spent lead-acid batteries may be extracted, purified,and used in the production of new lead-acid batteries. As illustrated inFIG. 1, the process 10 begins with processing (block 12) of spentlead-acid batteries (e.g., battery breaking) to generate a lead-bearingmaterial. For example, in an embodiment, one or more lead-acid batteriesmay be fed through a hammer mill or another suitable device that iscapable of crushing, pulverizing, grinding or otherwise physicallybreaking apart the entirety of the spent lead-acid battery. Thecomponents of the spent lead-acid battery may include, for example,metal posts, metal connectors, metal grids, carbon black, glass, aplastic or metal casing, plastic separators, plastic fibers, batterypaste (e.g., including various lead oxides, lead sulfates and leadcarbonates), and sulfuric acid, among other components. After beingsubstantially pulverized, the resulting battery component mixture may,in certain embodiments, be passed through one or more preliminarypurification steps in which certain components (e.g., the crushedplastic components) may be removed from the remainder of thelead-bearing material, for example, using a separation device that takesadvantage of the lower density of these plastic components. Further, incertain embodiments, some, or all, of the residual sulfuric acidentrained in the lead-bearing material may be recycled for reuse, orneutralized and crystallized as a solid sulfate for disposal or resale.In certain embodiments, pre-treatment of the lead-bearing material mayinclude a full or partial desulfurization stage in which the sulfatecontent of the lead-bearing material may be reduced by chemical means,for example, by treatment with a hydroxide (e.g., sodium hydroxide,NaOH) or carbonate (e.g., soda ash).

The illustrated method 10 continues with forming (block 14) a mixturethat includes a carboxylate source and the lead-bearing material. Forexample, to the lead-bearing material from block 12, a sodium citratesolution may be added to form such a mixture. In certain embodiments,water, and/or a hydroxide, and/or a peroxide, and/or acetic acid may beadded as well. In certain embodiments, the carboxylic source may bemetal citrate (e.g., sodium citrate), ammonium citrate, citric acid,metal acetate (e.g., sodium acetate), ammonium acetate, acetic acid, acombination thereof, or any other suitable carboxylic source that maydrive the formation of lead salts in the leaching mixture. In certainembodiments, this leaching step may be performed in a reactor, such as acontinuously stirred leaching tank, and may be performed at low (acidic)pH (e.g., pH between 1 and 7) and at slightly elevated temperatures(e.g., approximately 30-100° C.). The resulting mixture includes bothsoluble and insoluble residuals from the spent and pulverized batteries.Additionally, the carboxylic source in the mixture reacts with one ormore forms of lead in the mixture (e.g., metallic lead, lead sulfate,lead carbonate, and lead oxide), with or without the assistance of theperoxide and/or an acetate that may be present in the mixture, to yielda lead salt (e.g., lead citrate, lead acetate). Since the lead salt mayhave limited solubility in the mixture at these low pH levels, a leadsalt precipitate (e.g., a lead citrate precipitate, a lead acetateprecipitate) may be generated (block 16) in the mixture as a result.

However, as mentioned above, the lead salt precipitate present in themixture is also interspersed with residual insoluble components from thecrushed batteries. As such, continuing through the method 10, the pH ofthe mixture may be increased (block 18) to dissolve the lead saltprecipitate into the liquid component of the mixture. For example, incertain embodiments, the pH of the mixture may be increased aboveapproximately 7, above approximately 8, between approximately 8 andapproximately 14, or between approximately 8 and 12. In certainembodiments, this pH increase may be affected through the addition of ahydroxide. In certain embodiments, the hydroxide may be added slowly orall at once. Further, in certain embodiments, the pH increase of block18 may occur in a separate reaction vessel or reaction stage from thesteps of the preceding blocks.

Accordingly, once the lead salt precipitate has been dissolved in themixture, the liquid component of the mixture may be isolated (block 20)from the insoluble components of the mixture. For example, theseinsoluble components may include: barium sulfate, carbon black, glass,polymer, or a combination thereof. Additionally, the insolublecomponents may include residual metallic lead pieces from solid batteryparts (terminals, connectors, grids), composed of a lead alloy that mayinclude lead, antimony, arsenic, selenium, calcium, tin, silver,cadmium, or a combination thereof. In certain embodiments, theseresidual insoluble battery components may be filtered out or otherwiseisolated from the liquid component of the mixture. Further, one or moreof these insoluble components may be subsequently fed into othertreatment or purification systems and/or techniques in accordance withembodiments of the present disclosure.

Subsequently, the liquid component isolated in block 20 may, in certainembodiments, undergo an additional purification step before the leadsalt is precipitated and isolated. It should be noted that, forconsistency, the term “liquid component” is used throughout subsequentsteps to describe the liquid component initially isolated in block 20,even when this liquid is not part of a mixture (e.g., no solids present)and even as the liquid is modified throughout subsequent steps discussedbelow. With this in mind, the liquid component isolated in block 20 maybe mixed (block 22) with a compound that reacts with one or more solubleimpurities present in the liquid component to generate one or moreimpurity gases, which are then released from the liquid component. Ingeneral, the reactant is a reducing agent, such as a hydride source(e.g., sodium tetraborohydride, sodium hydride, hydrogen gas, orsyngas), that is capable of reacting with one or more soluble impuritiesin the liquid component to generate relatively volatile impurity gasesthat are subsequently vented from the liquid component. In general, theimpurities in the liquid component may include: elements and/orcompounds of Group 14 (e.g., carbonates, silicates, germanium salts,and/or tin salts), elements and/or compounds of Group 15 (e.g.,phosphates, arsenic salts, antimony salts, and/or bismuth salts),elements and/or compounds of Group 16 (e.g., sulfates, selenium salts,and/or tellurium salts), elements and/or compounds of Group 17 (e.g.,fluoride salts, chloride salts, bromide salts, and/or iodide salts), ora combination thereof. For example, the liquid component may includedissolved impurities that are chemical compounds (e.g., ionic saltsand/or covalent molecules) of tellurium, antimony, tin, selenium,arsenic, germanium, silicon, phosphorus, sulfur, or any combinationthereof. Accordingly, the reaction between these soluble impurities andthe aforementioned reactant may yield: hydrogen telluride, antimonytrihydride (stibine), tin tetrahydride (stannane), hydrogen selenide,arsenic trihydride (arsine), germanium tetrahydride (germane), siliconhydrides (silane), phosphine, hydrogen disulfide, or a combinationthereof. These and possibly other impurity gases released from theliquid component may be subsequently passed to other purificationtechniques or systems in accordance with the present disclosure. As aresult of the purification described in block 22, the liquid componentis purified from some or all of the aforementioned soluble impurities,resulting in a liquid component that is substantially a lead saltsolution (e.g., a lead citrate solution); however, some impurities(e.g., sodium sulfate) may still be present. In certain embodiments, thepurification described in block 22 may be skipped and the isolatedliquid component described in block 20 may directly advance to the nextstep (e.g., block 24) in the illustrated process 10. In certainembodiments, an alternative or additional step in the purification ofthe liquid component of block 20 may include the use of fine pure leadpowder for cementation of impurities on the surface of the leadparticles, and then this solid lead may be removed by a secondsolid/liquid separation stage.

Continuing through the process 10 illustrated in FIG. 1, the pH of theliquid component is decreased (block 24) in order to regenerate the leadsalt precipitate. For example, an acid or buffer salt (e.g., citricacid, acetic acid, sodium citrate, sodium acetate, etc.) may be added tothe liquid component to lower the pH to a value below 7 (e.g., betweenapproximately 1 and approximately 6.5, or between approximately 3 andapproximately 6) such that the solubility of the lead salt (e.g., leadcitrate, lead acetate) in the liquid component is decreased, causing thelead salt to once again precipitate from the solution. Subsequently,this lead salt precipitate may be isolated (block 26) from the liquidcomponent, for example, by filtration. After such a filtration, the leadsalt precipitate may be washed with water, and the filtrate and washwater may retain all or most of the remaining impurities separated fromthe lead salt precipitate. For example, in certain embodiments, theisolated lead salt precipitate may include little or no residualsulfates (e.g., sodium sulfate and/or lead sulfate), such as less than5% sulfates, less than 4% sulfates, less than 3% sulfates, less than 2%sulfates, less than 1% sulfates, less than 0.5% sulfates, less than 0.3%sulfates, or less than 0.1% sulfates. By specific example, FIG. 2presents an X-ray diffraction pattern representative of a lead saltprecipitate of the present approach in the form of a high purity leadcitrate product. Further, it may be appreciated that the filtrateliquids (e.g., the liquid component and water washes) may besubsequently passed to other purification techniques in accordance withthe present disclosure. Table 1, included below, provides chemicalanalysis data for an example input material (i.e., scrap battery paste,the lead-bearing material) and an example output material (i.e., arecovered lead citrate precipitate) as measured by ICP (inductivelycoupled plasma) spectrometry for an embodiment of the presentlydisclosed lead recovery method. Accordingly, Table 1 provides analyticaldata indicative of impurity levels in the lead bearing material and therecovered lead citrate salt for an embodiment of the present approach.From the values indicated in Table 1 it may be appreciated that, incertain embodiments, the recovered lead salt product (e.g., leadcitrate) may be substantially free of impurities.

TABLE 1 Chemical analysis of scrap battery paste (i.e., the lead-bearingmaterial) and an embodiment of the lead salt precipitate (i.e., leadcitrate) using inductively coupled plasma (ICP) spectroscopy. Indicatedvalues are listed in parts per million (ppm). Element Scrap BatteryPaste Lead Citrate Silver (Ag) 32 7 Arsenic (As) <1 <1 Barium (Ba) 348 8Bismuth (Bi) 90 7 Calcium (Ca) 189 11 Cobalt (Co) <1 <1 Chromium (Cr) <1<1 Copper (Cu) 9 1 Iron (Fe) 20 3 Manganese (Mn) <1 <1 Nickel (Ni) 2 <1Platinum (Pt) <1 <1 Sulfur (S) 35734 229 Antimony (Sb) 285 <1 Selenium(Se) <1 <1 Tin (Sn) 626 <1 Strontium (Sr) 4.9 0.5 Tellurium (Te) 1.7<0.3

Next in the process 10 illustrated in FIG. 1, the lead salt precipitatemay be treated (block 28) to yield leady oxide. In certain embodiments,the lead salt precipitate may be treated using calcination. For example,during a calcination-based treatment, the lead salt precipitate may beheated to a temperature less than 450° C. (e.g., between approximately275° C. and approximately 400° C., at approximately 330° C.), with orwithout presence of an additional oxidant (e.g., air, oxygen-enrichedair, gas stream containing oxygen bearing compounds) or an oxygenreducer (e.g. methane, coke, propane, natural gas, etc.), with orwithout addition of dopants to promote the formation of a preferred leadoxide crystal structure or particle morphology, such that the organicportion (e.g., citrate, acetate) combusts, resulting in a mixture offree lead (i.e., Pb(0)) and lead oxide (i.e., PbO), generally referredto as leady oxide. Examples of process controls for such calcinationtreatments that may affect the resulting leady oxide include: thetemperature of the calcination, time, droplet size, agglomerate size,residual moisture in the lead salt, the rate at which the lead salt isheated to the calcination temperature, introduction of a reducingsubstance, premixing with a second lead salt (lead formate, leadacetate) and/or introduction of additional inert gas (e.g., nitrogen).In other embodiments, the lead salt precipitate may instead be treatedwith base (e.g., a 25-50 wt % sodium hydroxide solution) and ahydroxylation/dehydration reaction between the base and the lead saltprecipitate may yield the desired leady oxide product. It may beappreciated that different methods of treating the lead salt precipitatemay provide different leady oxides (e.g., different crystal structures,different amounts of free lead, etc.). For example, treating the leadsalt precipitate with base may result in a leady oxide product havinglittle or no (e.g., approximately 0%) free lead. In certain embodiments,after removal of the solid leady oxide product from the basic solution,the basic solution may be subsequently treated to regenerate acarboxylate salt to be reused (e.g., in block 14) in the process 10.Optionally, the leady oxide may be further processed by washing, millingor grinding to obtain physical characteristics suitable for the intendeduse.

Using the disclosed process 10, the generated leady oxide may include,for example, between approximately 0% and approximately 35%, betweenapproximately 15% and approximately 30%, approximately 20%, orapproximately 30% free lead. Additionally, in certain embodiments, theleady oxide particles may have a D₅₀ (i.e., an indication of averagediameter, a diameter that is greater than the diameters of 50% of thesynthesized leady oxide particles) between approximately 0.2 μm andapproximately 4000 μm (e.g., between approximately 0.2 μm andapproximately 1 μm, between approximately 0.2 μm and approximately 20μm, between approximately 1 μm and 4000 μm). As such, it should beappreciated that the present approach may be useful for the synthesis ofleady oxide nanoparticles that are 200 nm or more in diameter.Additionally, in certain embodiments, the leady oxide particles may havea Brunauer-Emmett-Teller (BET) surface area greater than approximately1.0 square meters per gram (m²/g) (e.g., greater than approximately 1.0m²/g, approximately 1.5 m²/g, approximately 2.0 m²/g, or approximately2.5 m²/g). Further, in certain embodiments, the leady oxide may have anacid absorption greater than approximately 100 milligrams (mg), 200 mg,or 300 mg H₂SO₄ per gram. In certain embodiments, the leady oxide mayinclude less than approximately 20% beta phase lead oxide (β-PbO) (e.g.,less than 1% β-PbO), while in other embodiments, the leady oxide mayinclude greater than 80% β-PbO. FIG. 5 presents an X-ray diffractionpattern representative of a leady oxide product after a calcinationtreatment (in block 28), which demonstrates both PbO and Pb metal peaks.FIG. 6 presents an X-ray diffraction pattern representative of α-PbOlead oxide obtained by treatment of lead citrate with strong base. Assuch, it may be appreciated that the leady oxide particles formed by thepresent approach may enable the production of lead-acid batteries havinggood to excellent electrical performance.

The process 10 illustrated in FIG. 1 continues with the leady oxideproduced from the treatment of block 28 being formed (block 30) into aleady oxide active material for use in new lead-acid battery production.For example, the leady oxide may be mixed with water and sulfuric acidto form a battery paste that may be applied to a plurality of lead gridsto serve as the active material of a lead-acid battery. Accordingly, alead-acid battery may be constructed (block 32) using the leady oxidebattery paste formed in block 30. As mentioned above, the leady oxideactive material formed by the present approach may enable the productionof lead-acid batteries having good to excellent electrical performance.The leady oxide formed in block 28 may also be used to manufacturetribasic lead sulfate (3BS), tetrabasic lead sulfate (4BS), and red lead(lead (II,IV) oxide, Pb₃O₄). In the case of 3BS and 4BS, the materialsmay be produced by mixing the leady oxide formed in block 28 with waterand sulfuric acid in a heated stirred tank reactor. In the case of redlead, in certain embodiments, the material may be formed directly fromthe lead salt (e.g., lead citrate), or from the intermediate leady oxideof block 28, by calcination and oxidation at temperatures between 450and 500° C., for example.

FIG. 3 is a flow diagram illustrating an embodiment of a process 40 bywhich lead from spent lead-acid batteries may be extracted, purified,and used in the construction of a lead-acid battery. It may beappreciated that the process 40 illustrated in FIG. 3 is similar to theprocess 10 illustrated in FIG. 1; however, the process 40 illustrated inFIG. 3 includes fewer steps by delaying precipitation of the lead saltand, thereby, affording advantages in terms of efficiency. Like theprocess 10 illustrated in FIG. 1, the process 40 illustrated in FIG. 3begins with processing (block 12) of spent lead-acid batteries togenerate a lead-bearing material. As with block 12 of the process 10,this processing may include crushing and grinding the spent lead-acidbatteries and one or more preliminary purification steps discussed indetail above. However, from there, the process 40 illustrated in FIG. 3continues by forming (block 42) a basic mixture including a hydroxideand the lead-bearing material from block 12. For example, to thelead-bearing material from block 12, a hydroxide may be added to form abasic mixture. In certain embodiments, water, and/or a peroxide may beadded prior to, the hydroxide component. In certain embodiments, thismay be performed in a continuously stirred reactor, such as a leachingtank, at high pH (e.g., above 7, between 8 and 12) and slightly elevatedtemperatures (e.g., approximately 30 to 100° C.). The resulting mixtureincludes both soluble and insoluble residuals from the spent andpulverized lead-acid batteries. Additionally, the hydroxide in themixture is capable of reacting with one or more forms of lead in themixture (e.g., metallic lead, lead sulfate, lead carbonate, and leadoxide), with or without the assistance of peroxide that may be present,to yield a soluble lead salt.

Next, the liquid component of the mixture from block 42 may be isolated(block 44) from the insoluble components of the mixture. As discussedwith respect to block 20 in FIG. 1, these insoluble components mayinclude: barium sulfate, carbon black, glass, polymer, lead alloys, or acombination thereof. These insoluble components may be filtered orotherwise isolated from the liquid component of the mixture. Asdiscussed above, these insoluble components may be subsequently fed intoother lead purification systems and/or techniques.

Subsequently, the liquid component isolated in block 44 may optionallyundergo an additional purification like that described in block 22 ofFIG. 1. That is, continuing through the process 40 illustrated in FIG.3, the liquid component isolated in block 44 may be mixed (block 46)with a compound (e.g., a reducing agent, a hydride source such as sodiumtetraborohydride, sodium hydride, hydrogen gas, or syngas) capable ofreacting the one or more soluble impurities present in the isolatedliquid component to generate one or more impurity gases, which arereleased and/or separated from the liquid component. Consequentially,the liquid component is purified from some or all of these solubleimpurities, resulting in a liquid component that is substantially a leadhydroxide solution; however, some impurities (e.g., sodium sulfate,other metal hydroxides) may still be present. In certain embodiments,block 46 may be skipped and the isolated liquid described in block 44may directly advance to the next step (e.g., block 48) in theillustrated process 40.

Continuing through the process 40 illustrated in FIG. 3, a carboxylatesource (e.g., citrate or acetate) may be added (block 48) to the liquidcomponent to decrease the pH of the liquid and to generate a lead salt(e.g., lead citrate, lead acetate) precipitate. For example, a citrate(e.g., citric acid) may be added to the mixture to react with the leadcompound in solution to form a lead citrate precipitate. Further, sincethe carboxylate source decreases the pH of the liquid below 8 (e.g.,between approximately 2 and approximately 7), the solubility of thegenerated lead salt decreases, causing the lead salt to precipitate. Aswith the previously discussed method 10, the lead salt precipitateresulting from block 48 of the process 40 illustrated in FIG. 3 may besubstantially pure and may include little or no sulfates (e.g., lessthan 5% sulfates, less than 4% sulfates, less than 3% sulfates, lessthan 2% sulfates, less than 1% sulfates, or less than 0.1% sulfates).After the lead salt precipitate is formed, the remainder of the process40, including the steps of isolating the lead salt precipitate (block26), treating the lead salt precipitate to form the leady oxide (block28), forming the leady oxide into an active material (block 30), andconstructing lead-acid batteries (block 32), are substantially the sameas described above with respect to the method 10 illustrated in FIG. 1.As mentioned above with respect to the process 10, the leady oxideactive material formed by the process 40 enables the production of newlead-acid batteries having good to excellent electrical performance.

FIG. 4 is a flow diagram illustrating an embodiment of a process 60 bywhich lead from spent lead-acid batteries may be extracted, purified,and used in the construction of a lead-acid battery. It may beappreciated that the process 60 illustrated in FIG. 4 is similar to theprocess 10 illustrated in FIG. 1; however, the process 60 illustrated inFIG. 4 includes the use of an antisolvent to promote the precipitationof the lead salt prior to isolation. Several of the steps of theillustrated process 60 are the same as the steps of the process 10,discussed above, and, as such, the present discussion will highlight thedifferences between the two processes. In particular, as illustrated inFIG. 4, after performing the actions described in blocks 12, 14, 16, 18,20, and 22, the purified liquid component may include a dissolved leadsalt (e.g., lead acetate, lead citrate). In the process 10, discussedabove, a carboxylate source may be added (FIG. 1, block 24) to decreasethe pH of the liquid component to cause the dissolved lead salt toprecipitate. In contrast, for the process 60 illustrated in FIG. 4, anantisolvent may be added (block 62) to cause the dissolved lead salt toprecipitate. For example, the antisolvent may be a solvent or acombination of solvents whose molecular structure includes a non-polarhydrocarbon portion as well as a polar portion containing a hetero atomsuch as oxygen, sulfur, or nitrogen. By specific example, a non-limitinglist of antisolvents may include: methanol, ethanol, propanol, ethyleneglycol, or combinations thereof.

After adding the antisolvent to the liquid component in block 62, thelead salt precipitate may be isolated from the liquid component in block26, after which the lead salt precipitate may proceed to the actionsdescribed in blocks 28, 30, and 32. In contrast to the previouslydiscussed processes, since an antisolvent replaces the pH adjustment tofacilitate precipitate of the lead salt, the liquid component that isisolated from the lead salt precipitate in block 26 remains at a high pHvalue. Accordingly, in certain embodiments, the liquid componentisolated in block 26 may proceed through a distillation step to recoverthe antisolvent from the remainder of the liquid component, and therecovered antisolvent may then be recycled back into process at block62. Furthermore, after recovering the antisolvent via distillation, thehigh pH liquid component may be recycled back into the process 60. Forexample, in certain embodiments, this recovered, high-pH liquidcomponent may be recycled into the leaching mixture formed in block 14to facilitate leaching of the lead solids. By further example, incertain embodiments, this recovered high-pH liquid component may berecycled into block 18 to raise the pH of the mixture of block 18 anddissolve the lead salt precipitate formed in block 16. Accordingly, theaforementioned recycling may improve the efficiency of the process 60,when compared to the process 10, by avoiding the neutralization step ofblock 24 of the process 10, which limits the amount of base and acid(e.g., hydroxide and carboxylate source) consumed during the process 60.

One or more of the disclosed embodiments, alone or on combination, mayprovide one or more technical effects useful in the recycling oflead-acid batteries and/or in the recovery and purification of lead fromwaste materials. Embodiments of the present approach enable theindustrial scale extraction and purification of lead from spentlead-acid batteries. Further, present embodiments enable the removal ofseveral impurities (e.g., insoluble impurities, sulfates, alloyingmetals) from the recovered lead, thereby avoiding or reducing theformation of certain undesired combustion byproducts as well as the costassociated with scrubbing these byproducts from the exhaust stream. Thetechnical effects and technical problems in the specification areexemplary and are not limiting. It should be noted that the embodimentsdescribed in the specification may have other technical effects and cansolve other technical problems.

While only certain features and embodiments of the disclosure have beenillustrated and described, many modifications and changes may occur tothose skilled in the art (e.g., variations in sizes, dimensions,structures, shapes and proportions of the various elements, values ofparameters (e.g., temperatures, pressures), mounting arrangements, useof materials, colors, orientations) without materially departing fromthe novel teachings and advantages of the subject matter recited in theclaims. The order or sequence of any process or method steps may bevaried or re-sequenced according to alternative embodiments. It is,therefore, to be understood that the appended claims are intended tocover all such modifications and changes as fall within the true spiritof the disclosure. Furthermore, in an effort to provide a concisedescription of the exemplary embodiments, all features of an actualimplementation may not have been described (i.e., those unrelated to thepresently contemplated best mode of carrying out the invention, or thoseunrelated to enabling the claimed invention). It should be appreciatedthat in the development of any such actual implementation, as in anyengineering or design project, numerous implementation specificdecisions may be made. Such a development effort might be complex andtime consuming, but would nevertheless be a routine undertaking ofdesign, fabrication, and manufacture for those of ordinary skill havingthe benefit of this disclosure, without undue experimentation.

1. A method, comprising: reacting one or more impurities of a lead saltsolution with at least one compound to evolve one or more impurity gasesthat are released from the lead salt solution, wherein the one or moreimpurities comprise an element or compound of Group 14, an element orcompound of Group 15, an element or compound of Group 16, an element orcompound of Group 17, or a combination thereof.
 2. The method of claim1, wherein the one or more impurities comprise tellurium, antimony, tin,selenium, arsenic, germanium, silicon, phosphorus, sulfur, or acombination thereof.
 3. The method of claim 1, wherein the at least onecompound comprises sodium tetraborohydride.
 4. The method of claim 1,wherein the at least one compound comprises sodium hydride.
 5. Themethod of claim 1, wherein the at least one compound comprises hydrogengas.
 6. The method of claim 1, wherein the at least one compoundcomprises syngas.
 7. The method of claim 1, wherein the at least onecompound is a reducing agent that reduces at least one impuritydissolved in the solution.
 8. The method of claim 1, wherein the one ormore impurity gases comprise hydrogen telluride, antimony trihydride(stibine), tin tetrahydride (stannane), hydrogen selenide, arsenictrihydride (arsine), germanium tetrahydride (germane), silicon hydrides(silane), phosphine, hydrogen disulfide, or a combination thereof. 9.The method of claim 1, comprising acidifying the lead salt solutionafter the one or more impurity gases have been released to form a leadsalt precipitate and then isolating the lead salt precipitate.
 10. Themethod of claim 9, comprising treating the lead salt precipitate usingcalcination or a base treatment to form leady oxide particles.
 11. Themethod of claim 10, wherein the leady oxide particles comprise betweenapproximately 0% and approximately 35% free lead.
 12. The method ofclaim 10, wherein the leady oxide particles have a D₅₀ value betweenapproximately 0.2 μm and approximately 20 μm.
 13. The method of claim10, wherein the leady oxide particles have a Brunauer-Emmett-Teller(BET) surface area greater than approximately 2.5 square meters per gram(m²/g).
 14. The method of claim 10, wherein the leady oxide particleshave an acid absorption greater than approximately 250 milligrams H₂SO₄per gram.
 15. The method of claim 10, wherein the leady oxide comprisesless than approximately 20% beta phase lead oxide.
 16. The method ofclaim 10, comprising: forming an active material for use in a lead-acidbattery, wherein the active material comprises leady oxide purified fromthe solution; and constructing a battery comprising the active material.17. The method of claim 10, wherein the lead salt precipitate compriseslead citrate, lead acetate, lead hydroxide, or a combination thereof.18. A method, comprising: (A) forming a mixture comprising a carboxylatesource and a lead-bearing material; (B) generating a first lead saltprecipitate in the mixture as the carboxylate source reacts with thelead-bearing material; (C) increasing the pH of the mixture to dissolvethe first lead salt precipitate; (D) isolating a liquid component of themixture from one or more insoluble components of the mixture; (E) addingan antisolvent to the liquid component to generate a second lead saltprecipitate; and (F) isolating the second lead salt precipitate from theliquid component of the mixture.
 19. The method of claim 18, wherein theantisolvent comprises: methanol, ethanol, propanol, ethylene glycol, orcombinations thereof.
 20. The method of claim 18, comprising: (G)recovering the antisolvent from the liquid component via distillation.21. The method of claim 20, comprising: (H) recycling the antisolventinto step (E) to generate a second lead salt precipitate.
 22. The methodof claim 20, comprising: (H) recycling the liquid component into step(A) to facilitate leaching of lead solids.
 23. The method of claim 20,comprising: (H) recycling the liquid component into step (C) to increasethe pH of the mixture.